The present invention relates to high-density semiconductor devices, and in particular, to a mask for and method of forming a character on a substrate of a semiconductor device that is visible by an observer without aid of magnification even when the character is formed on a substrate having complex and random patterns.
Etching processes are commonly used in semiconductor manufacturing technology to transfer patterns to semiconductor substrates for the purpose of forming circuits on the substrate. A standard illuminator arrangement used in the patterning process is depicted in FIG. 1. The illuminator arrangement 100 includes a radiation concentrator 110, such as an elliptical mirror, that reflects energy emitted by radiation source 120 into the entrance pupil of the illuminator, i.e., input lens 130. The illuminator of the exposure tool may employ intensity randomizer 140, which randomizes the intensity of the radiation in the illuminator. Intensity randomizer 140, for example a fly-eye lens, is used in the microlithography exposure tool illuminator in order to insure light intensity uniformity at the projection lens entrance. The exposure tool illuminator may also employ a partial coherence aperture 150, which reduces the undesirable impact of the peripheral regions of the intensity randomizer on the uniformity of the illumination.
The physical size of the randomizer 140 or the size of the opening in the partial coherence aperture 150 defines the area (size) of the effective light source of the projection system that is used to form the image of reticle 170 on wafer 190. Condenser lens 160 focuses the effective light source onto the entrance pupil of projection lens 180 through reticle 170. Projection lens 180 projects the pattern contained in reticle 170 onto the photoresist layer of the wafer 190.
In the typical etching process of semiconductor devices, a protective etching mask or photoresist layer is first formed employing a layer of photoresist material (xe2x80x9cresistxe2x80x9d) disposed on a major surface of the semiconductor device. This protective resist etch mask is designed to facilitate the formation of a desired pattern of lines and spaces (resist areas) in the resist layer based on a predetermined etch pattern. Thus, when an optical source, such as UV light, passes through the reticle and contacts these predetermined resist areas, the predetermined etch pattern is created in the resist structure which exposes the requisite portions of the semiconductor surface for subsequent etching purposes. Once the protective etching resist mask is in place on the semiconductor surface, etching of the exposed areas can commence to produce a semiconductor having a predetermined etched pattern.
One of the first resist materials used in semiconductor fabrication produced a negative image and thus was called a negative resist. In a negative resist, areas where the optical source strikes becomes polymerized and more difficult to remove. When the resist is xe2x80x9cdevelopedxe2x80x9d (subjected to a solvent), the polymerized regions remain and the unpolymerized areas are removed. A second, and more commonly used, etching process is called a positive resist. Positive resists are based on a totally different chemistry than negative resists. In a positive resist etching process, exposure to an optical source changes the positive resist material so that it is solubilized and can be more easily removed. Since the exposed regions are removed, the resist is referred to as positive.
Once the circuitry of the semiconductor device is formed, it can be difficult to distinguish one particular semiconductor device from another. Accordingly, there is a need for a mask for and method of forming a character on a substrate of a semiconductor device that is visible by an observer without aid of magnification. The character could be used to distinguish one semiconductor device from another. Due to the existence of complex and random patterns on the substrate of the semiconductor devices, the mask and method should be designed to form a distinguishing character that is clearly visible on semiconductor devices having preexisting patterns.
The present invention relates to a mask and method to form a character on a substrate of a semiconductor device that can be clearly observed even if positioned over complex and random patterns formed on the substrate.
The mask of the present invention is used during an etch process to form a readable character on a surface of a substrate of a semiconductor device that is visible by an observer without magnification. The mask includes a medium that is generally transparent and a region that provides a character (or indicia). The region includes one or more plurality of regions that each includes a plurality of gratings or lines. The gratings are generally opaque, thereby providing a contrast between the region and a remainder of the medium. The gratings are configured to form a character (or indicia) that contrasts with the remainder of the medium.
The region of the exemplary embodiment includes a first region formed by a plurality of first gratings or lines and a contrasting second region formed by a plurality of second gratings or lines. In the exemplary embodiment the first and second gratings include a plurality of parallel lines with transparent spaces evenly arranged between the lines. The first gratings are generally oriented in a direction that is non-parallel to the direction of the second gratings. The non-parallel arrangement of the first grating and the second grating provides a contrast therebetween. The preferred embodiment of the present invention utilizes the contrast between two different gratings to create a character, such as an alphanumeric symbol, or some other symbol, shape, logo, icon, etc.
When light is passed through the mask, the light is refracted off the gratings, thereby producing markedly different colors and/or intensities of light on the substrate. The image formed on the substrate is easily seen at 1X magnification by an observer when viewed under normal, broad spectrum, visible light.
The present invention includes a method of manufacturing a semiconductor device using the mask described above. The method includes a step of coating a substrate with a photosensitive material. The method further includes a step of projecting light through a mask onto the coating. The mask used in the process is that described above and it includes a region having a character (or other indicia) within the region. The mask is used to project an image onto the substrate of the semiconductor device. The method includes a step of removing a portion of the coating based upon exposure to the light. The portion of the coating that is removed is based upon whether a negative resist or a positive resist is used and depends upon whether it is desired to positively or negatively etch the character into the substrate. The method also includes a step of etching exposed portions of the substrate that are not covered by a remaining portion of the coating to form a character visible by an observer without aid of magnification. The result of the method set forth above is a substrate of a semiconductor device that has a character formed on a surface of the substrate, which can be used to identify a particular semiconductor device.
Additional advantages and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. The advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.